Uric acid (UA) is an end-product of purine derivatives in human metabolism. Without further metabolism, it is excreted by kidneys and intestinal tract. Its serum concentration is controlled by the balance between production and excretion. High concentration of UA in human body has been discovered to be associated with various diseases, such as gout, hyperuricaemia, Lesch-Nyan disease, obesity, diabetes, high cholesterol, hypertension, kidney disease and heart disease. This book discusses the detection, applications and role in health and disease of uric acid.